--- title: "Evolution from telegraphy to fiber and wireless" subject: "Telecommunications" chapter: 1 key: "semester_8/telecommunications:evolution-telegraphy-to-fiber" source: https://www.bctengineer.com/q/semester_8/telecommunications/evolution-telegraphy-to-fiber site: BCT Engineering --- # Evolution from telegraphy to fiber and wireless Telecommunications · Chapter 1: Telecommunication Networks - Asked in: 2081 Bhadra, 4+4 marks - Video: [The Bottleneck Breakthrough: The Complete Evolution of Telecommunication | Telegraph to 5G & Beyond](https://www.youtube.com/watch?v=JupxfoEih18) — Technology Verse - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/evolution-telegraphy-to-fiber - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-1 ## Question Discuss the evolution of telecommunication technology from the early days of telegraphy to modern-day fiber optics and wireless communication. What were the key technological breakthroughs that shaped this evolution? ## Short answer Telegraphy, telephony, wireless, multiplexing, digital transmission (PCM), electronic switching, optical fibre (low-loss, EDFA, DWDM), and mobile/cellular. Key breakthroughs: Morse code, telephone transmitter, Strowger switch, vacuum tube/transistor, PCM, satellites, laser and low-loss fibre, cellular concept, packet switching and TCP/IP. ## Answer Telecommunication has moved from sending simple on/off electrical pulses over wires to sending terabits of data over glass fibre and radio. Each stage was made possible by a key technical breakthrough. #### Evolution 1. **Telegraphy (1837–1870s):** Morse's electric telegraph and Morse code; undersea telegraph cables (transatlantic 1866). First fast long-distance communication, but only text and only between offices. 2. **Telephony (1876 onward):** Bell's telephone carried voice; manual exchanges (1878), then Strowger automatic exchanges (1892) and crossbar systems. 3. **Wireless telegraphy and radio (1895–1920s):** Marconi's spark transmitter; transatlantic radio (1901); vacuum-tube amplifiers and oscillators led to AM broadcasting and radiotelephony. 4. **Multiplexing and long-haul (1920s–1950s):** FDM carrier systems on open wire and coaxial cable; microwave line-of-sight relays (1940s–50s) carried thousands of calls and TV. 5. **Digital transmission (1960s):** PCM and T1/E1 TDM systems; Telstar and later geostationary satellites (Intelsat, 1965) for intercontinental links. 6. **Electronic and digital switching (1965–1980s):** SPC exchanges, digital TDM exchanges, common channel signalling (SS7), ISDN. 7. **Optical fibre (1970s–now):** low-loss fibre (1970), semiconductor lasers, SDH/SONET, erbium-doped fibre amplifiers (EDFA, ~1990) and DWDM, giving terabit capacity and undersea fibre cables. 8. **Wireless/mobile (1979–now):** 1G analogue cellular, 2G GSM digital (1991), 3G, 4G LTE, 5G; Wi-Fi, and Internet over mobile. #### Key technological breakthroughs - **Morse code and electromagnetic relay** – practical electrical signalling. - **Telephone transmitter/receiver and carbon microphone** – voice over wires. - **Strowger switch** – automatic switching without operators. - **Vacuum tube (1906) and transistor (1947)** – amplification, then cheap reliable electronics; later **integrated circuits and microprocessors** enabling SPC and digital systems. - **PCM and sampling theory (Nyquist, Shannon)** – digital voice, TDM and error-free regeneration. - **Satellites (1962–65)** – global coverage. - **Laser (1960) and low-loss fibre (1970)** – huge bandwidth with very low loss; **EDFA and WDM** multiplied capacity. - **Cellular concept (frequency reuse, handover)** – mobile telephony for millions. - **Packet switching and TCP/IP** – the Internet and all-IP networks. These breakthroughs together took telecom from a few words per minute to billions of bits per second. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which breakthroughs made optical fibre systems high-capacity? A. Triode valves and coaxial cable B. Strowger selectors and rotary dials C. Low-loss fibre (1970), lasers, EDFA and DWDM D. Spark transmitters and crystal detectors Answer: C. Low-loss fibre and lasers gave bandwidth, while EDFA and WDM multiplied capacity. (Key point: Fibre) 2. Why were PCM and sampling theory key breakthroughs? A. They allowed operators to connect calls faster B. They made wireless telegraphy possible C. They gave frequency reuse for mobiles D. They allowed digital voice, TDM and error-free regeneration Answer: D. Digital signals can be regenerated without noise build-up. (Key point: PCM) 3. What concept made mobile telephony available to millions? A. The cellular concept, with frequency reuse and handover B. Using a single powerful transmitter C. The Strowger switch D. Message switching at telegraph offices Answer: A. Reusing frequencies in cells and handing over calls serves many users. (Key point: Cellular) 4. What was the breakthrough of the Strowger switch? A. Transmitting voice over wires B. Automatic switching without operators C. Amplifying signals D. Digitising speech Answer: B. It removed the need for an operator. 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